This invention relates to knives of the kind having a blade which is movable between an extended or operative position and a retracted or inoperative position. It is usual for the blade to be contained within a handle of the knife when retracted, and the invention will be hereinafter described with particular reference to that form of knife.
Retractable blade knives of the foregoing kind are generally constructed so that a worn or damaged blade can be removed and replaced by a new blade. Example constructions of that kind are disclosed by U.S. Pat. Nos. 3,577,637, 3,593,417 and 4,242,795. It is not convenient to sharpen the blade in knives of the foregoing kind and as a result blade replacement may occur or be required at relatively short intervals of time.
It has been proposed in the past to provide a retractable blade knife with a self-sharpening facility, and U.S. Pat. No. 1,890,506 (Frank) discloses that particular construction. The Frank knife is not known to have been manufactured in commercial quantities, and is distinguished from the other retractable blade knives referred to above in that the blade is not readily replaced. It has the further disadvantage in that retraction of the blade extends rather than reduces the overall size of the knife. The Frank knife is also not satisfactory because the self-sharpening facility does not sharpen the entire length of the blade cutting edge, and in particular does not and cannot sharpen the very tip of the blade which is often the most used portion of the blade.
Another common problem with knives of the foregoing kind is that the blade is not firmly restrained in the extended position so that pressure on the blade during use can cause unintentional retraction of the blade.
It is an object of the present invention to provide a knife of the foregoing kind which has an effective self-sharpening facility. It is another object to provide such a knife having means to prevent inadvertent extension of the blade. It is a further object to provide such a knife with means whereby the blade is positively retained in the extended position.